PSI - Issue 28

Rita Dantas et al. / Procedia Structural Integrity 28 (2020) 796–803

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Rita Dantas et al. / Structural Integrity Procedia 00 (2019) 000–000

Nomenclature � maximum shear stress on the critical plane � number of cycles to failure ��� reference number of cycles to failure � ��� endurance limit at ��� � negative inverse slope of the modified Wöhler curve ��� effective value of the critical plane stress ratio � � normal mean stress to the critical plane � � normal stress amplitude to the critical plane m mean stress sensitivity index R stress ratio �∗ , �∗ � , �∗ � shear and normal stress components to the critical plane of an endurance limit with R >-1 � � estimated number of cycles to failure material fatigue constants � endurance limit for fully reversed uniaxial loading � � endurance limit for fully reversed torsional loading negative inverse slope of the fully reversed uniaxial loading modified Wöhler curve � negative inverse slope of the fully reversed torsional loading modified Wöhler curve ��� limit value of ��� � tensile strength � yield strength E young modulus µ mean σ standard deviation 1. Introduction Fatigue is a critical degradation process affecting engineering structures and it is believed to be responsible for half of the failures of mechanical components. In particular, multiaxial fatigue is frequently observed in engineering applications, such as wind turbines or offshore structures, not only due to complex loading scenarios, but also due to notches and geometries that originate a multiaxial stress state in the presence of uniaxial loadings (Kamal & Rahman, 2018). Therefore, around the middle of the twentieth century, a couple of different models and approaches which aimed at addressing the multiaxial fatigue problem were developed and studied such as the models presented by Gough and Pollard, Findley, Sines and Matake (Findley, 1958; Gough & Pollard, 1935; Matake, 1977; Sadek & Olsson, 2016; Sines, 1955, 1959). Nowadays, in spite of these models’ wide and spread application, new ones have been formulated and multiaxial fatigue remains an open topic. Some of these new modern models are: Dang Van’s multi-scale approach, which proposes a model based on the interaction between macroscopic and mesoscopic scales, Papadopoulos’ and Carpinteri-Spagnoli’s models, which propose complex approaches for hard metals, and Susmel’s model, which will be presented throughout this work (Carpinteri & Spagnoli, 2001; Dang-van, 1993; I. V. Papadopoulos, 1994). Hence, this work aims at comprehending and evaluating the ability of Susmel’s model to assess the fatigue behavior of S355 steel in high-cycle fatigue region and under proportional loading. Therefore, experimental fatigue data from previous researches were re-analysed and used to assess this multiaxial fatigue model under study as well as to determine fatigue design curves for each loading condition. Finally, the index errors between experimental and theoretical fatigue damage were calculated and analysed. This assessment has focused on proportional loading with constant amplitude, so that material mechanisms related to more complex loadings, such as non-proportional or variable amplitude, will be left for future researches and works.